Oscilloscopes have for many years provided multiple input channels and a means for calibration of those channels in terms of gain and course frequency response adjustments. However, as bandwidths extend into the GHz region it becomes more and more difficult to provide a flat response at all frequencies. Some oscilloscope manufactures have incorporated a high frequency control DAC used to tune the 3 dB bandwidth point of each channel. However, this only controls a band of high frequency with a general gain control for the whole band, as opposed to controlling the gain at each frequency. Thus the flatness of each individual scope channel bandwidth varies by several dB as a function of frequency. In addition there are differences in frequency response between channels that can be significant in some applications.
Scopes have also traditionally made adjustments in calibration at manufacturing in order to match channels as much as possible. Some of the adjustments made include DC offset, gain, and time skew. The match between scope channels is adequate for many applications. However, applications such as using two channels to look at a differential signals are limited by the degree of mismatch in current generation oscilloscopes.